Update test.md

Author: HsiangNianian

blog/test.md

@@ -9,4 +9,27 @@ featuredpath: img/post
 draft: false
 showtoc: true
 ---
-## Test
+## Test
+
+```jsx live
+function Clock(props) {
+  const [date, setDate] = useState(new Date());
+  useEffect(() => {
+    const timerID = setInterval(() => tick(), 1000);
+
+    return function cleanup() {
+      clearInterval(timerID);
+    };
+  });
+
+  function tick() {
+    setDate(new Date());
+  }
+
+  return (
+    <div>
+      <h2>It is {date.toLocaleTimeString()}.</h2>
+    </div>
+  );
+}
+```